In plants having duct systems in which gas processing equipment are incorporated, it is a requirement that such equipment may be isolated by dampers from the gas stream when servicing is required.
As the cross sectional dimensions of such ducts are large, the cost of such dampers is necessarily substantial particularly where the blades of the dampers must be of a high quality nickel alloy steel. The blades must meet certain functional requirements which depend on such factors as differential pressures and temperatures to which they are to be subjected as well as the nature of the hot gas streams and particles carried thereby.
By way of example, duct systems where the duct sections are fifteen feet by fifteen feet, require that damper blades of a high quality nickel alloy steel be at least one and five-sixteenth inches in thickness with a resulting blade weight of approximately 14,000 pounds and with a blade materia1 cost, at the present time of about ten dollars a pound to the damper manufacturer, at least $140,000. In addition, such a blade has high transportation costs and requires that the cost of the mechanism by which such a blade is reciprocated between duct blocking and open positions be proportionally large.